The present invention relates to an alumina powder characterized by having a single or multiple crystal structure selected from the group consisting xcex3, xcex4 and xcex8-forms, a primary particle size of 10 to 50 nm, a mean secondary particle size (mean aggregated particle size) of 100 to 500 nm, and a granular primary particle:shape, an alumina powder characterized by having an xcex1-form crystal""structure, a primary particle size of 60 to 150 nm, a mean secondary particle size (mean aggregated particle size) of 200 to 500 nm, and a granular primary particle ""shape, and processes for producing those. The present invention also relates to polishing compositions using those alumina powders as an abrasive.
The polishing compositions of the present invention can efficiently provide a smooth polished surface with high precision in polishing an aluminum disk, and therefore are useful as a final finish polishing composition. The xe2x80x9cpolishing an aluminum diskxe2x80x9d intended herein means to polish the surface of a substrate itself of a magnetic memory disk comprising aluminum or its alloy, the surface of a layer of, for example, non-electrolysis nickel-phosphornus (Nixe2x80x94P) plating or non-electrolysis nickel-boron (Nixe2x80x94B) plating, formed on the substrate, particularly a hard layer of non-electrolysis nickel-phosphorus (Nixe2x80x94P) plating having compositions comprising 90 to 92% Ni and 8 to 10% P, and the surface of an aluminum oxide layer.
Further, the polishing material using an abrasive of alumina according to the present invention can efficiently provide a smooth polished surface with high precision, and therefore is useful for polishing an oxide film, a nitride film or carbide film of a semiconductor device, a wiring metal of a semiconductor multilayer wiring substrate, or the like, and for final finish polishing a magnetic head, a quartz, a glass and the like.
Alumina powder comprising alumina fine particles having a mean particle size of 1 xcexcm or less is produced by dry and/or wet grinding alumina having a crystal structure of, for example, xcex3, xcex4, xcexa, xcex8, xcex7 or xcex1-form obtained by calcining aluminum hydroxide that is produced by the Bayer process at low cost and in large amount.|
Further, high purity alumina powder of a plate-like, xcex3-form, xcex4-form or the like crystal structure having a primary particle size of 20 to 80 nm or high purity alumina powder of xcex1-form crystal structure having a primary particle size of 150 to 200 nm or more is commercially available.
Further, EP-A-0554908 (corresponding to JP-A-5-345611 (1993)) describes xcex1-form alumina having a primary particle size of 20 to 50 nm in which a barrier of silica is formed around boehmite particles to thereby suppress growth of particles in transferring to xcex1-form alumina.
Further, JP-A-7-089717 (1995) discloses a process for producing alumina sol of, for example, xcex3, xcex4, xcexa, xcex8, xcex7 or xcex1-form, having a mean particle size of 100 nm or less by a peptization method of contacting commercially available ultrafine alumina powder as it is, or a powder obtained by calcining the ultrafine alumina powder, with a cation-exchange resin in an aqueous phase in the presence of an acid.
A slurry obtained by mixing water, an alumina polishing material, and a polishing accelerator, and if necessary, a surface modifier, is used as a polishing composition which is used in polishing an aluminum disk. As the examples of this polishing accelerator, U.S. Pat. No. 4,705,566 (corresponding to JP-B-2-023589 (1990)) disclosed aluminum nitrate, nickel nitrate, nickel sulfate, and the like, and JP-A-2-158682 (1990) discloses sodium nitrite, potassium nitrite, calcium nitrite, magnesium nitrite, barium nitrite, zinc nitrite, aluminum nitrite or the like.
In recent years, performance of aluminum disk has the tendency of gaining higher density and higher speed. Therefore, no surface defect of orange peel, scratch, pit, asperity or the like, and high flatness with small mean surface roughness and small maximum surface roughness are strongly demanded.
The alumina powder having a crystal structure of, for example, xcex3, xcex4, xcexa, xcex8, xcex7 or xcex1-form obtained by calcining and grinding aluminum hydroxide produced by the Bayer process has a broad particle size distribution due to the break-down method even if the alumina powder comprises alumina fine particles having a mean particle size of 1 xcexcm or less. For this reason, a wet classification (hydraulic elutriation or the like) is conducted, but it is difficult to completely remove coarse particles. Where a polishing material having coarse particles intermixed therein is used, it is difficult to obtain a polished surface of high quality.
Further, in the alumina powder having a crystal structure of xcex3 or xcex4-form obtained by calcining aluminum hydroxide produced by a metal alkoxide method, the particle shape is plate-like. Therefore, the material to be polished is in the state that the material slides on a pad during polishing, and a removal rate is slow, so that productivity of polishing step is poor. Furthermore, since the alumina powder having a crystal structure of xcex1-form has a primary particle size of 150 to 200 nm or more , it is difficult to obtain a polished surface of high quality.
Further, in the xcex1-form alumina having a barrier of silica as the surface layer and having a primary particle size of 20 to 50 nm, the removal rate thereof is slow due to the silica layer having a removal rate slower than that of alumina.
On the other hand, alumina sol of, for example, xcex3, xcex4, xcexa, xcex8, xcex7 or xcex1-form having a mean particle size of 100 nm or less by a peptization method of contacting commercially available ultrafine alumina powder as it is, or a powder obtained by calcining the ultrafine alumina powder, with a cation-exchange resin in an aqueous phase in the presence of an acid has a primary particle size of 10 nm or less. Therefore, the removal rate is slow and productivity of polishing step becomes poor.
The present invention has an object to provide alumina powders as an abrasive suitable for a polishing composition which can improve productivity of polishing step and decrease cost by increasing the removal rate while maintaining the polished surface of high quality, a process for producing those alumina powders, and a polishing composition.
The present inventors have found an alumina powder having a single or multiple crystal structure selected from the group consisting of xcex3, xcex4 and xcex8-forms, a primary particle size of 10 to 50 nm, wherein the particle size distribution is sharp, a mean secondary particle size (mean aggregated particle size) of 100 to 500 nm, and a granular primary particle shape, obtained by calcining alumina hydrate comprising rectangular plate-like primary particle having a length of one side of 10 to 50 nm and having a boehmite structure as a raw material by the production process of the present invention without using commercially available alumina powder and grinding, and an alumina powder having an xcex1-form crystal structure, a primary particle size of 60 to 150 nm in which the particle size distribution is sharp, a mean secondary particle size (mean aggregated particle size) of 200 to 500 nm, and a granular primary particle shape obtained by the same process and the same raw material. The present inventors have also found that if the alumina powder of the present invention is used as an abrasive in a polishing composition for aluminum disk, comprising an abrasive, water and a polishing accelerator, a polished surface of higher quality can be obtained as compared with the conventional polishing material for aluminum. disk, and the alumina powder has high speed polishing property.
In addition, the present inventors have found that if an alumina mixed abrasive is prepared by adding the alumina powder having a single or multiple alumina crystal structure selected from the group consisting of xcex3, xcex4 and xcex8-forms, a primary particle size of 10 to 50 nm, a mean secondary particle size (mean aggregated particle size) of 100 to 500 nm, and a granular primary particle shape to the alumina powder having an xcex1-form crystal structure, a primary particle size of 60 to 150 nm, a mean secondary particle size (mean aggregated particle size) of 200 to 500 nm, and a granular primary particle shape, or to an alumina powder having an xcex1-form crystal structure, a primary particle size of 50 nm to 2 xcexcm, and a mean secondary particle size of 200 nm to 3xcexcm obtained by calcining and grinding the commercially available aluminum hydroxide produced by the Bayer process, and then mixing those, a polished surface of higher quality can be obtained by polishing, and a polishing material for aluminum disk having high speed polishing property can be formed on polishing
A production process of the alumina powder that is characterized by having a single or multiple crystal structure selected from the group consisting of xcex3, xcex4 and xcex8-forms, a primary particle size of 10 to 50 nm, a mean secondary particle size (mean aggregated particle size) of 100 to 500 nm, and a granular primary particle shape comprises the following steps (A), (B), (C) and (D):
(A) a step of adding an alkali to an aqueous alumina sol containing fibrous colloidal particles of amorphous alumina hydrate to form a reaction mixture having pH of 9 to 12;
(B) a step of subjecting the reaction product obtained in step (A) to hydrothermal treatment at 110 to 250xc2x0 C. to form an aqueous suspension containing alumina hydrate having boehmite structure;
(C) a step of drying the aqueous suspension obtained in step (B) at 100xc2x0 C. or more and then calcining the same at 500 to 1,130xc2x0 C. to form alumina having a single or multiple crystal structure selected from the group consisting of xcex3, xcex4 and xcex8-forms; and
(D) a step of dry and/or wet1grinding the alumina obtained in step (C).
The alumina powder having xcex4-form crystal structure, a primary particle size of 10 to 50 nm, a mean secondary particle size of 100 to 500 nm, and a granular primary particle shape, wherein the polishing property is more preferable, is obtained by calcining at 850 to 1,050w in step (C).
A production process of the alumina powder is characterized by having an xcex1-form crystal structure, a primary particle size of 60 to 150 nm a mean secondary particle size of 200 to 500 nm, and a granular primary particle shape comprises the following steps,(A), (B), (C) and (D):
(A) a step of adding an alkali to an aqueous alumina sol containing fibrous colloidal particles of amorphous alumina hydrate to form a reaction mixture having pH of 9 to 12;
(B) a step of subjecting the reaction product obtained in step (A) to hydrothermal treatment at 110 to 250xc2x0 C. to form an aqueous suspension containing an alumina hydrate having boehmite structure;
(C) a step of drying the aqueous suspension obtained in step (B) at 100xc2x0 C. or more and then calcining the same at 1,150 to 1,300xc2x0 C. to form alumina having an xcex1-form crystal structure; and |
(D) a step of dry and/or wet grinding the alumina obtained in step (C).
Considering productivity and polishing properties, it is preferable that alumina powder characterized by having an xcex1-form crystal structure, a primary particle size of 60 to 150 nm, a mean secondary particle size of 200 to 500 nm, and a granular primary particle shape is calcined at 1,180 to 1,250xc2x0 C. in step (C).
The polishing composition for aluminum disk comprises an abrasive of alumina, water and a polishing acceleratory. The abrasive of alumina comprises the alumina powder characterized by having a single or multiple crystal structure selected from the group consisting of xcex3, xcex4 and xcex8-forms, a primary particle size of 10 to 50 nm, a mean secondary particle size of 100 to 500 nm, and a granular primary particle shape; the alumina powder characterized by having an xcex1-form crystal structure, a primary particle size of 60 to 150 nm, a mean secondary particle size of 200to 500 nm, and a granular primary particle shape; or a mixture of the alumina powder having a single or multiple crystal structure selected from the group consisting of xcex3, xcex4 and xcex8-forms, a primary particle size of 10 to 50 nm, a mean secondary particle size of 100 to 500 nm, and a granular primary particle shape, and the alumina powder having an xcex1-form crystal structure, a primary particle size of 50 nm to 2 xcexcm, a mean secondary particle size of 200 nm to 3 xcexcm.
The polishing accelerator is preferably a basic salt formed from a trivalent or tetravalent metal and an inorganic or organic acid. As the trivalent or tetravalent metal, aluminum is more preferable. Of the inorganic acid or organic acid, nitric acid is more preferable in polishing property. Basic aluminum nitrate is more preferable. The further more preferable is basic aluminum nitrate represented by the chemical composition of Al(OH)x(NO3)3-x (wherein x is a real number of 0.5-2.7).
The production process of the alumina powder of the present invention is described in detail below.
In step (A), the aqueous alumina sol containing fibrous colloidal particles of amorphous alumina hydrate used in step (A) is easily obtained by the conventional production process, and is available as commercially available industrial chemicals. JP-B-45-003658 (1970) and JP-A-60-166220 (1985) disclose a process for producing an aqueous alumina sol containing fibrous colloidal particles of amorphous alumina hydrate by reacting an aqueous solution of an organic acid and a metallic aluminum powder under heating. The aqueous alumina sol obtained by those conventional production processes of aqueous alumina sol :can also be exemplified.
The aqueous alumina sol as the raw material is not limited so long as it does not form a gel, and sols comprising from ones having low viscosity of several mPaxc2x7s to ones having high viscosity of several hundreds of thousand mPaxc2x7s can be used. In particular, an aqueous alumina sol having Al2O3 concentration of 2 to 30 wt % and pH of 2 to 7 is preferable. Further, since formation of a bulk of gel material or rise in viscosity is induced depending on the addition method of an alkali, it is further preferable that the Al2O3 concentration of the aqueous alumina sol is previously adjusted to 2 to 4 wt % at the time of adding the alkali.
In a reaction mixture having pH of less than 9 obtained by adding an alkali, the objective acidic aqueous alumina sol containing alumina hydrate having boehmite structure cannot be obtained even if hydrothermal treatment of the next step is conducted. On the other hand, even in a reaction mixture having pH exceeding 12 obtained by adding excess alkali, the objective aqueous alumina suspension containing alumina hydrate having boehmite structure can be obtained. However, the excess alkali must be removed in step (B), which is not preferable. Therefore, it is more preferable for the reaction mixture obtained by adding an alkali to have pH of 9 to 12.
In step (B), if the reaction product is subjected to hydrothermal treatment at a temperature of less than 110xc2x0 C. long time is required for the formation of a crystal structure of from fibrous colloidal particles of an amorphous alumina hydrate to rectangular plate-like primary particles of the alumina hydrate having a boehmite structure in an aqueous suspension, which is not preferable. On the other hand, in the hydrothermal treatment reaction exceeding 250xc2x0 C., a quenching equipment, ultrahigh pressure vessel or the like is necessary as an additional apparatus, which is not preferable.
In order to decrease the contents of salts in the aqueous suspension, desalting treatment can be conducted by an ultrafiltration or an ion exchange method., In step (C), if calcined at a temperature of less than 500xc2x0 C. , the boehmite particles remain unchanged. Further, in the case of calcining at a temperature exceeding 1300xc2x0 C. particle growth of particles having xcex1-form crystal structure is vigorous, so that the primary particles become 150 to 200 nm or more, surface roughness is large, and orange peel, scratch, pit and asperity increase, which are not preferable.
In step (D), if dry and/or wet grinding is insufficient, the secondary particles are larger than 500 nm, so that surface roughness is large, :and orange peel, scratch, pit and asperity increase, which are not preferable.
The alumina powder according to the present invention, which has a single or multiple crystal structure selected from the group consisting of xcex3, xcex4 and xcex8-forms, is an alumina powder having a primary particle size of 10 to 50 nm and a mean secondary particle size of 100 to 500 nm, obtained by dry and/or wet grinding such as vibration mill, ball mill, attritor or sand grinder. This alumina powder uses alumina hydrate having a boehmite structure of controlled particle size as a raw material, and therefore a particle size distribution is sharp.
The alumina powder having an; xcex1-form crystal structure of the present invention is an alumina having a primary particle size of 60 to 150 nm and a mean secondary particle size of 200 to 500 nm, obtained by dry and/or wet grinding such as vibration mill, ball mill, attritor or sand grinder. This alumina powder uses alumina hydrate having a boehmite structure of controlled particle size as a raw material, and therefore a particle size distribution is sharp.
The primary particle size of alumina powder intended here is individual primary particle size measured by observing the primary particles with a transmission electron microscope, and is not a mean particle size.
The mean secondary particle size of alumina powder is a median particle size (50% volume particle size) showing a mean aggregated particle size. Commercially available centrifugal particle size distribution measuring apparatus, such as CAPA-700, manufactured by Horiba, Ltd., is used for the measurement thereof.
The polishing composition of the present invention is described in detail below.
The content of the abrasive of alumina in the polishing composition is 0.5 to 20 wt %. If the content of the abrasive of alumina is less than 0.5wt %, the polishing effect is small, and if the content is increased to exceed 20 wt %, further improvement in the polishing effect is not recognized.
In the alumina powder having a single or multiple crystal structure selected from the group consisting of xcex3, xcex4 and xcex8-forms, a primary particle size of 10 to 50 nm, a mean secondary particle size of 100 to 500 nm, and a granular primary particle shape, the preferable crystal structure is xcex4-form crystal structure. ;
In the alumina powder mixture of the alumina powder having a single or multiple crystal structure selected from the group consisting of xcex3, xcex4 and xcex8 forms, a primary particle size of 10 to 50 nm, a mean secondary particle size of 100 to 500 nm, and a granular primary particle shape, and the alumina powder having an xcex1-form Crystal structure, a primary particle size of 50 nm to 2 xcexcm, a mean secondary particle size of 200 nm to 3 xcexcm, the weight ratio of the alumina solid content (a) of a single or multiple crystal structure selected from the group consisting of xcex3, xcex4 and xcex8-forms and the alumina solid content (b) of xcex1-form crystal structure is preferably a:b=5:95 to 70:30, and more preferably 5:95 to 50:50. In the group consisting of xcex3-, xcex4- and xcex8-form alumina powders, xcex4-form alumina powder is preferable. If the xcex4-form alumina powder is used in the above alumina powder mixture, a ratio ((Vp/Ra) of a removal rate (Vp) to a mean surface roughness((Ra) as polishing characteristics becomes high, which is preferable.
Zirconia, zirconium silicate, silica, mullite, cerium oxide, iron oxide, chromium oxide, titanium oxide and the like which are oxides can be added together with the alumina powder. Hydroxides such as aluminum hydroxide, hydrated oxide such as boehmite; and non-oxides such as diamond, boron nitride, silicon nitride, silicon carbide or boron carbide can also be added.
The polishing accelerator is preferably a basic salt formed from a trivalent or tetravalent metal and an inorganic or organic acid. Examples of the trivalent metal include aluminum, indium and iron, and examples of the tetravalent metal include zirconium, cerium, tin and titanium. Examples of the inorganic acid include nitric acid and sulfuric acid, and examples of the organic acid include acetic acid, formic acid, sulfamate, tartaric acid, oxalic acid and gluconic acid. As the trivalent or tetravalent metal, aluminum is excellent. As the inorganic acid and organic acid, nitric acid is excellent in the polishing properties. Basic aluminum nitrate is more preferable. The further more preferred is basic aluminum nitrate represented by the chemical composition of Al(OH)x(NO3)3-x (wherein x is a real number of 0.5 to 2.7). The most preferable is Al(OH)(NO3)2.
The polishing accelerator content is preferably 0.1 to 10 wt % when expressed in a reduced concentration of metal oxide M2O3 (wherein M represents a trivalent metal: atom) in a basic salt formed from the trivalent metal and the inorganic acid or organic acid, and when expressed in a reduced concentration of metal oxide MO2 (wherein M represents a tetravalent metal atom) in a basic salt formed from the tetravalent metal and the inorganic acid or organic acid. If the content is less than 0.1 wt %, the effect as the polishing material is not recognized, and if the content is increased to exceed 10 wt %, further improvement of the effect as the polishing accelerator is not recognized. The content is more preferably 0.3 to 6 wt %.
Further, water-soluble alcohols such as ethanol, propanol, ethylene glycol or propylene glycol; acids such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid or phosphoric acid; surface active agents such as sodium alkylbenzenesulfonate or formalin condensate; organic polyanion type substances such as polyacrylate; and celluloses such as cellulose, hydroxyethyl cellulose or carboxymethyl cellulose, which are generally added to the polishing composition can also be added to the polishing composition.
The analytical methods employed in the present invention are as follows.
(1) pH Measurement
Measured using a pH meter (M-8AD, manufactured by Horiba, Ltd.).
(2) Electric Conductivity
Measured using a conductometer (CM-30S, manufactured by TOA Electronics Ltd.).
(3) Primary Particle Size and Primary Particle Shape
Primary particle size and primary particle shape were observed with a transmission electron microscope.
Observation method: A sample was diluted with pure water, and the sample was coated on a hydrophilic carbon-coated collodion film placed on a microscope sample grid of copper, and then dried to prepare a sample for observation. An electron micrograph of the sample for observation was taken with a transmission electron microscope (H-500, manufactured by Hitachi, Ltd.) to observe the sample.
(4) Mean Secondary Particle Size
Median particle size (50% volume size) was measured using a centrifugal sedimentation particle size measuring apparatus (CAPA-700, manufactured by Horiba, Ltd.) to determine a mean secondary particle size (mean aggregated particle size).
(5) Particle Size by Dynamic Light Scattering Method
Measured using an apparatus for measuring a particle size by dynamic light scattering method (Culter N4 (registered trademark), manufactured by Culter Electronics, Inc.).
(6) Specific Surface Area (BET Method)
A sample previously dried under the prescribed conditions was measured using a specific surface area meter of nitrogen gas absorption method (MONOSORB Model MS-16, manufactured by Quantachrome Corp.).
(7) Powder X-ray Analysis
Measured using an X-ray diffraction device (JEOL JDX-8200T, manufactured by JEOL Ltd.)